Electrographic devices for the development composition and transfer of particles images

ABSTRACT

Device for producing electrographic images from an original provided with a conductivity pattern of conductive and less conductive areas, said original coated with a layer of developer particles and interposed between two insulating layers. An electric field is generated to charge and remove away from the conductivity pattern a part of the particles leaving an electrographic image on the original. This original may consist in a photoconductive layer exposed to an electromagnetic radiation.

United States Patent June 17, 1975 Cantarano ELECTROGRAPHIC DEVICES FOR THE 2.758.525 8/1956 Moncrieff-Yeates 355m x DEVELOPMENT COMPOSITION AND 2.924.519 2/1960 Bertelsen 96/1 R TRANSFER OF PARTICLES IMAGES 2.968.552 1/1961 Gundlach ll7/l7.5 X 3.071.645 1/1963 McNaney 355/17 X [76] Inventor: Marcus Cantarano, 47 Ave. F. 3.1 .418 5 Roosevelt Thiais Fran e 3.l66.420 Clark l. X 3.185.051 5/1965 Goffe 96/13 X Flled: p 16, 1973 3.707.138 l2/l972 Cartwright 96/L4 x Primary E.raminerRobert P. Greiner [60] Division of Ser. No. 870.405. Dec. 8. 1969. Pat. No. 57 ABSTRACT 3.741.761. which is a continuation-in-part of Ser. No. D 63mm April 8 1967 abandoned. ev ce for producing electrograph ic images from an original provided with a conductivity pattern of con- [52] Cl I I I I 355/3 355/17. 7/175. ductive and less conductive areas. said original coated 96/] with a layer of developer particles and interposed be- [5 I] Int Cl. 4 15/0'0 tween two insulating layers. An electric field is gener- [58} Field 96/! R ated to charge and remove away from the conductivity 6 1 [7H7 pattern a part of the particles leaving an electrographic image on the original. [56] References Cited This original may consist in a photoconductive layer UNITED STATES PATENTS exposed to an electromagnetic radiation. 2.758.524 8/1956 Sugarman 355/17 X 24 Claims, 11 Drawing Figures 2 l l T I LSSOOISS PATENTEDJUN 17 I975 SHEET 1 ELECTROGRAPHIC DEVICES FOR THE DEVELOPMENT COMPOSITION AND TRANSFER OF PARTICLES IMAGES This application is a division of application Ser. No. 870,405, filed Dec. 8, 1969, now Pat. No. 3,741,761. which application in turn is a continuationin-part of application Ser. No. 631.792, filed Apr. 8, 1967, now abandoned.

This invention relates to the production of electrographic images from an original provided with a conductivity pattern, to the production of an electro graphic image and to the transfer or the obtained images on to sheets of webs of copy material.

As used herein, the term conductivity pattern is to be understood as including any virtually plane surface formed by parts having different electric conductivities.

In the following specification, the term insulating is to be understood as defining the quality of having an electric conductivity lower than l mho/cm and the term noninsulating" as defining the quality of having an electric conductivity superior to lOmho/cm.

In the actual art, a feature of electrographic methods resides in the use of an original provided with a conductivity pattern including high insulating parts which will selectively hold electric charges to form a latent electrostatic image; thus an electrographic image may be developed by an electrically responsive powder which adheres to the charged parts of the latent image. This electrographic image will not be obtained in a stable way because of the passage of electric charges even through the high insulating parts of the original causing the effacement of at least a part of the latent image during the step of the development. A typical original of actual electrography consists in a photoconductive insulating layer provided with a conductivity pattern resulting from an exposure to a light image; such a photoconductive layer will be a high insulator in the dark in order to obtain a conductivity pattern including the non-illuminated high insulating parts serving to develop an electrographic image according to existing methods. These photoconductive insulating layers are slow in their response to successive different exposures to the light and, consequently, they may not be used to afford high speed processes to produce successive different electrographic images. Furthermore, these insulating layers having a very low sensitivity to the light, the enlarging of a document is still difficult to obtain in electrography.

l have found, however, that a stable electrographic image may be formed and simultaneously developed in the absence of a latent electrostatic image; to this end an original is used which is provided with a pattern of conductive and less conductive parts affixed to an insulating backing material, the conductivity pattern of the original is coated with a thin layer of developer powder, an insulating layer is placed against the layer of powder and an electric field is generated to charge the powder from said conductivity pattern and to electrically remove a part of the coating powder; whereby a stable electrographic image is formed on the least conductive parts of said pattern by the remaining coating powder which is never sufficiently charged to be removed. The present invention thus relates to the production of stable electrographic images from an original provided with a conductivity pattern affixed to an insulating backing material, to the development of stable electrographic images from an original consisting in a photoconductive layer excited by a light image. to the development of a stable electrographic image from a photoconductive layer successively excited by different light images, and to the transfer of the obtained images on to sheets or webs of copy material.

A feature of the present invention resides in the use of an original provided with an insulating backing material carrying a conductivity pattern including noninsulating conductive parts, the minimal conductivity of this pattern being not critical to develop a stable electrographic image according to the invention. Furthermore, l have found that a stable electrographic image may be developed from an original consisting in an insulating backing material carrying a photoconductive layer provided with a conductivity pattern including illuminated non-insulating parts resulting from an exposure to a light image. Such a photoconductive layer can be called photoconductive non-insulating layer because of its electric conductivity superior to 10""mho/cm when illuminated. These photoconductive non-insulating layers are to be distinguished from the photoconductive insulating layers of classic electrography. In carrying out this invention, a photoconductive non-insulating layer may be used which has a virtually instantaneous response and a high sensitivity to the light as, for example, a layer of cadmium sulfide or cadmium selenide, or other high sensitive layers commonly used in the photoresistive cells.

According to the present invention, the conductivity pattern of the original is coated with a thin layer of developer powder, an insulating layer is placed against the layer of powder and an electric field is generated to charge the powder from said conductivity pattern pattern; because of the insulating of the coated conductivity pattern between the insulating backing of the original and said insulating layer, the coating powder will receive electric charges having maximum values in proportion with the conductivities of said pattern; under the action of the electric field a part of the coating powder will be electrically attracted away from the original, while the powder coating the least conductive parts of said pattern is never sufficiently charged to be removed and it develops a stable electrographic image thereon. This method is well adapted to produce the dense large areas as well as the half-shadow areas of the electrographic image. By using an original provided with a pattern having high differences in conductivity, this method is well adapted for the high speed production of stable electrographic images; to this end a direct electric field may be generated to obtain each stable electrographic image in less than 1 millisecond; by using an original consisting in a photoconductive noninsulating layer, this stable image is generally obtained in less than 25 milliseconds, this lack of time including the light and dark responses of the layer when it is exposed to successive different light images. On the other hand, by generating an alternatively modulated electric field transferring alternating charges from the pattern of the original to the coating powder, this method is well adapted to produce stable electrographic images from an original provided with a pattern having low differences in conductivity; the amplitude of the modulated field is then adjusted to attract particles of powder having successive opposite polarities away from the most conductive parts of said pattern while the powder coating the least conductive parts of said pattern is never sufficiently charged to be removed; because of the opposite charges of these particles, the removal of the powder may be prosecuted to electrically attract away all the powder coating the most conductive parts of said pattern, while the remaining part of the coating powder develops a stable electrographic image of high density on the least conductive parts of said pattern.

According to a further embodiment of the invention. an original is used which consists in a photoconductive non-insulating layer provided with a conductivity pattern resulting from an exposure to a light image, the photoconductive layer is coated with a thin layer of developer powder, an insulating layer is placed against the layer of powder, an electric field is generated to charge the powder from the conductivity pattern and to remove a part of the coating powder leaving a stable electrographic image on the least conductive parts of said pattern, and, thereafter, a sheet of copy material is placed against the powder of the electrographic image, the photoconductive non-insulating layer is excited to a uniform high conductivity by a uniform exposure to a light of high intensity, and a second electric field is generated to charge powder from the excited photoconductive non-insulating layer; whereby, under the combined action of the electric field and of the light, the charged powder image is transferred on to the sheet of copy material.

An object of this invention is to improve electrographic methods and to provide means and devices for use in electrography.

Another object of this invention is to provide methods and means for the advantageous use of photoconductive non-insulating layers in electrography.

Other objects of this invention will be apparent from the following description and accompanying drawings taken in connection with the appended claims.

In the drawings:

FIG. 1 is a sectional view showing a development device comprising an original between two electrodes;

FIG. 2 is a schematic representation showing the electrographic image developed in the device illustrated in FIG. 1;

FIG. 3 is a sectional view showing a development and transfer device comprising an original and a sheet of copy material between two electrodes;

FIG. 4 is a schematic representation showing two grains of developer powder against the original of the device illustrated in FIGS. 1 and 3;

FIG. 5 is a schematic representation showing two grains of developer powder against a photoconductive layer exposed to a light image;

FIG. 6 is a sectional view showing a development device comprising a photoconductive layer exposed to a light image;

FIG. 7 is a schematic representation showing a development device comprising an original and a powderer;

FIG. 8 is a schematic representation showing grains of powder on the photoconductive layer of the development device of FIG. 7;

FIG. 9 is a sectional view showing a transfer device comprising a uniformly excited photoconductive layer and a sheet of copy material, between two electrodes;

FIG. I is a schematic representation of an apparatus serving to the development and the transfer of electro' graphic images;

FIG. 11 is a schematic representation of another embodiment of the apparatus illustrated in FIG. 11.

In the arrangement shown in FIGS. I to 4, for producing electrographic images an original I provided with indicia 2 having another electric conductivity than the surface 3 of the backing material 1] is disposed between two electrodes 6 and 7. Owing to the differences of electric conductivity between the materials of the parts I I and 2 of original 1, the latter is provided with a conductivity pattern formed by the areas 2 of the indicia and by the blank surface 3 of the backing l]. The

l() indicia 2 may be of different types as typewriting,

China ink or pencil traces, for example. Furthermore, if continuous tone electrographic images are to be produced, an original 1 will be used which is provided with differently conductive indicia 2 forming dense areas 5 and half-shadow areas as like as a photographic picture. On the other hand, as FIGS. 5 to 7 show, an original 1 may be used which consists in a photoconductive layer 24 provided with a conductivity pattern 2, 3 resuiting from the exposure of layer 24 to a light image;

the pattern 2, 3 is then formed by the illuminated con ductive parts 2 and the low illuminated low conductive parts 3 of the layer 24. In order to produce the light image on the layer 24, a transparent electrode 7 is used which consists, for example, in a thin layer of NESA,

25 a high conductive transparent varnish sold by Pittshurg Plate Glass Co., Pittsburgh, Pa. The layer of NESA may be supported by a transparent glass plate I7, for example. The light sources 4! illuminate a document 2I to be reproduced; the light is reflected by document 21 toward objective 31 and is transmitted across the trans' parent electrode 7 and the transparent backing 44 of layer 24 to form the optical image of document 21 on the photoconductive layer 24. Document 2] may be a sheet of paper carrying printed or typewritten matter, or drawing, for example, although other things may be photographed such as three-dimensional objects, for example. Alternatively, other radiations than light may be used to form the pattern 2, 3 such as, for example,

X-rays or gamma-rays; furthermore, any other means inducing in the layer 24 a pattern of conductive parts 2 and low conductive parts 3 may be used to produce electrographic images according to invention. On the other hand, when, for example, a X-rays image 2, 3 is formed on the layer 24, a sheet of aluminium may constitute the transparent electrode 7, for example.

In the preferred form of this invention a layer 24 of a photoconductive non-insulating material is used which has a high sensitivity and a virtually instantaneous response to the light. Alternatively, many photoconductive non-insulating materials may be used such as, for example, metallic selenium, thallium sulfide, cadmium sulfide, cadmium selenide, lead sulfide. In general, the sensitivity to the light of the layers of these non-insulating materials is from the 200 microamp/lumen of layers of metallic selenium to the 1000 milliam/lumen of cadmium selenide layers. The spectral response of metallic selenium is from the ultra-violet to the red part of the spectrum with maximum sensitivity in the ultra-violet, cadmium sulfide has virtually the same spectral response than human eye with maximum sensitivity between yellow and green, lead sulfide has maximum sensitivity in the infra-red from 2 to 3.5 microns of wave length. Alternatively and for example, lead sulfide, lead telluride or lead selenide layers may be used according to the invention to photograph objects emitting invisible light from 2 to 20 microns of wave length. The use of layers having maximum sensitivity in the visible part of the spectrum permit to reduce the losses in the transmission of light across the lens, mirrors etc. of the optical devices serving to form the ight image to be reproduced. Moreover. cadmium selenide is well adapted for the high speed production of copies from successive different light images, the responses of this material to the light and to the dark being shorter than milliseconds. On the other hand, when less than four electrographic images per second are to be produced from a high contrastfull light image, a usual in the art photoconductive insulating layer affixed to a backing electrode may be used, in spite of the low sensitivity of this type of photoconductive layer; although, a photoconductive insulating layer may be used which is constituted by a thin metallic layer of about 5 microns of gold or tellurium affixed to an insulating backing and by a photoconductive layer of 50 microns of amorphous selenium evaporated on said thin metallic layer.

As FIGS. 1 and 6 show, the conductivity pattern 2, 3 of original 1 is coated with a developer powder 5. If the grains size of powder 5 is from l to microns, the thickness of the layer of powder 5 will be about 50 microns, for example. For the uniform application of the powder 5, classic spraying or cascading devices may be used, provided that a thin uniform layer of powder 5 is formed rather than a particular amount of grains. In carrying out the invention it is expedient to use a developer powder 5 having an electric conductivity between the maximum and the minimum conductivities of the parts forming the pattern 2, 3 of the original, although the exact conductivity of the powder 5 is not critical in order to produce satisfactory electrographic images. Alternatively, metallic or semi-conductive or thermoplastic powders have been found useful. By way of example, charcoal, stannous oxide, lead sulfide, cadmium selenide as well as other colored materials may be powdered to be used as developers. The grains size of the powder may be between I and 40 microns, for example.

In the arrangement shown in FIGS. 1 and 6, a powder-coated original I is disposed between the electrode 7 and a second electrode 6 in the form of a grid. The thin layer of developer powder 5 is insulated from the grid 6 by a fluid dielectric consisting, for example, of an air layer 4. The grid 6 may be made of brass and have a mesh width of about 0.5 mm, for example; the spacing between grid 6 and original 1 may be from I to 4 mm, for example. The layer of powder 5 is applied loosely-adhering to the pattern 2, for example, this adherence of powder 5 may be obtained by previously coating the pattern 2, 3 with a slight adhesive material as well as through the use of a powder 5 the grains of which are rendered slight adhesive by a thin zinc stearate or aluminium stearate coat, for example. Any other means to obtain a loosely-adherence of powder 5 to the pattern 2, 3 may be useful in carrying out the present invention. Under the influence of an electric field generated between electrodes 6, 7, the powder 5 is electrically charged and removed from the conductive parts 2, while the powder coating the low conductive parts 3 is never sufficiently charged to electrically overcome its adherence to the parts 3 and thus it develops a stable electrographic image thereon. The intensity of the electric field cannot exceed 3.3 v/micron in the layer of air 4 to avoid a sudden electric discharge between electrode 6 and layer of powder 5; which would reduce the electric field serving to the development of the image. Instead of this, the quality of the electrographic image is improved by generating between electrodes 6 and 7 an electric field having, in the air layer 4, a gradient between 2.5 and 3.1 v/micron to obtain a silent ionizing discharge in the air 4 simultaneously with the development of the electrographic image, in this manner the powder 5 will be electrically charged from the slight conductive air 4 to adhere to the low conductive parts 3, while the electric field remains sufficiently intense, in the air 4, to electrically charge and remove the coating powder from the conductive parts 2. Instead of the air 4, other insulating gas as well as insulating liquids may be used as fluid dielectric 4, such as, for example, a silicone oil having a high electric rigidity of about 25 v/micron. What matters is that the coating powder 5 is insulated from the electrode 6 and that the layer 4 permits the passage of the grains of powder attracted away from the original during the development; these grains thus migrate through the openings of the grid 6 and they are definitively removed from the electric field. Furthermore, in accordance with the present invention, when a direct field is generated between electrodes 6 and 7, the conductivity pattern 2, 3 is to be insulated from electrode 7 to prevent any direct electric currents filtering through the low conductive parts 3 from electrically charging and removing away even the part of the powder which serves to develop the stable image over the original. The insulation of the pattern 2, 3 may be constituted by the insulating backing II, 44. If, on the contrary, the backing of the original is made of a low insulating material such as, for example, a sheet 11 of ordinary paper, a dielectric is to be arranged between the sheet II and electrode 7. This dielectric may be consti tuted by a sheet of MYLAR having a thickness of microns, for example.

According to an embodiment of the invention, electrographic images are produced by applying an alternating voltage to electrodes 6 and 7; to this end the terminals 9 are connected, for example, across the coil 29 of an adjustable electric transformer I9. Referring to this embodiment, FIGS. 4 and 5 schematically show two grains l2, 13 of the coating powder 5 placed against the conductivity pattern 2, 3 of the original 1. The adherence of the grains to the pattern 2, 3 is indicated by the arrows b. Because of the different conductivities of the parts 2 and 3, the contact conductance r between grain I2 and the conductive part 2 is higher than the contact conductance r between the grain I3 and the low conductive parts 3. By generating an alternating electric field between electrodes 6 and 7, grains l2 and 13 will receive alternating electric charges having different maximum values according to the different contact conductances r and r under the action of the field, the charged grains 12 and 13 are repelled from original 1 by modulated forces having maximum values a and a-,, in substantial proportion to the contact conductances r and r respectively; the amplitude of the alternating voltage is then adjusted to apply, to grain 12, a force a more intense than its adherence b to the original 1, whereby the grain 12 is electrically attracted through grid 6, while, because of the alternating character of the charges of powder 5, the electric force a is never sufficiently intense to overcome the adherence of the grain 13 to the low conductive part 3. A stable electrographic image is thus obtained by the powder 13 on the parts 3 of original I. Generally, a satisfactory image is developed by generating two or three complete periods of the alternating field; although, the electrographic image being obtained in a stable way, its good quality is irrespective of a longer duration of the electric field and of a slight electric conductivity of the parts 3. By way of example, if a photoconductive insulating layer 24 of amorphous selenium having a conductivity of about lU mho/cm is used as original I, an alternating field from 0.2 to 4 Hz may be generated to obtain stable images; when a photoconductive insulating layer 24 is used which has a conductivity from I to about lO' mho/cm, the frequency of the field will be from 5 to 60 H2. If a photoconductive layer 24 is used which has an electric conductivity superior to those cited above, the frequency of the alternating field will be higher than I00 H2. In this case the spacing between electrode 6 and the coating powder 5 is reduced, for example, at 0.5 mm to avoid that the charged grains 12 fall again on original I, which would deteriorate the electrographic image during its development. On the other hand, instead of grid 6, a compact electrode 6 may be used which is coated with a high insulating ma terial such as a polyvinyl resin, for example; by using this arrangement of parts the charged grains 12 will electrically adhere to the insulating coat of electrode 6 in spite of the electric action of the successive opposite polarities of the alternating field.

According to another embodiment using the devices of FIGS. I, 3, 6 and 7, an original I is used which is provided with an insulating backing ll, 44 having an electric conductivity lower than about lO 'mho/cm. such as a sheet of MYLAR, for example. By applying an alternating or an alternatively modulated voltage to terminals 9, the coating powder 5 receives, from the pattern 2, 3 alternating electric charges having maximum values in proportion to the conductivities of said pattern; the amplitude of the alternating modulation of the voltage is adjusted to electrically attract the powder 12 away from the conductive parts 2 while the powder I3 develops a stable electrographic image on the low conductive parts 3. According to this embodiment, it is expedient the use of an original 1 provided with parts 2 having an electric conductivity higher than 10 mho/cm and a thickness from I to ID microns. Because of the insulation of the pattern 2, 3 from the electrode 7, electric currents filtering through the low conductive parts 3 are avoided and thus the frequency of the developing electric field may be maintained as low as 10 or 60 Hz, for example. The amplitude of the modulated field is then adjusted to attract particles 12 of powder having successive opposite polarities away from the most conductive parts 2 of original 1, while the powder 13 coating the least conductive parts 3 is never sufficiently charged to be removed; because of the opposite charges of the particles I2 attracted away from the original 1, the removal of powder I2 may be prosecuted to electrically remove all the powder coating the most conductive parts 2, while the remaining part 13 of the coating powder develops a stable electrographic image of high density. This method is well adapted to produce satisfactory electrographic images from an original I provided with a pattern 2, 3 having low differences in conductivity such as, for example, a CDSEX7 layer 24 of cadmium selenide excited by a light image having a maximum intensity of about 0.6 lux and a minimum intensity of about 0.2 lux; the light image induces in the CDSEX7 layer a maximum con ductivity about 6 orders in magnitude higher than its minimum conductivity. Moreover, the best quality of continuous tone electrographic images is obtained by using a layer 24 which has a photoelectric linear character such as, for example a layer CDSH35 of cadmium sulfide, the linear feature of this layer residing in the proportionality between its electric conductivity and the intensity of the exciting light. Contrastful electrographic images may be obtained when the CDSH35 layer 24 is exposed, for example, to a light image rendering the parts 3 about 5 orders in magnitude less conductive than the parts 2, the minimum illumination of parts 2 being ().I lux for example. On the other hand, a direct voltage may be applied to terminals 9 to produce stable images from a contrastful original I provided with parts 2 at least 30 orders in magnitude more conductive than low conductive parts 3, such as, for example, a sheet of insulating paper carrying China ink traces, an electrographic image may be obtained by applying an impulsion of direct voltage during 0.] or I millisecond, for example. Although, the image being developed in a stable way, a longer duration of the electric field is not critical in order to obtain satisfactory results. By applying said direct voltage, electrographic images of good quality may be produced from a CDSEX7 layer 24 excited by a light image having a minimum intensity of about 2.5 lux and a maximum intensity of 20 lux, for example; the response of the CDSEX7 layer to light (20 lux) is about 4 milliseconds, its response to the dark (2.5 lux) is about 15 milliseconds. Furthermore, the sensitivity to light of layer 24 may be improved by applying a high electric potential ofa suitable polarity to this layer; thus the sensitivity of a selenium layer 24 may be improved by applying, for instance, L000 volts of positive potential to layer 24; to this end, the electrode 7 may be grounded, an electronic valve 49 and a condenser 39 are used to apply said positive potential to layer 24 through the electrode 6 and the ionized air 4, and an electric transformer I9 induces an alternating signal in the secondary coil 29 to alternatively modulate the direct voltage in order to develop satisfactory electrographic images according to the invention.

The devices illustrated with reference to FIGS. 1 and 6 can be used to develop two stable electrographic images simultaneously from the same original 1. To this end, as shown in FIG. 3, an insulating sheet of copy material 8 is placed against the layer of powder 5 to intercept the powder 12 electrically removed from the conductive parts 2 during the development of the powder image 13; whereby a first stable electrographic image is developed on the sheet of copy while a second electrographic image 13 is developed on the low conductive parts 3 of original 1. For example, a sheet of paper may be used as copy material 8. The original 1 may be constituted, for instance, by a photoconductive layer exposed to a light image accordingly to the method described with reference to FIG. 6. Satisfactory electrographic images may be developed by using an original 1 provided with a pattern 2, 3 having a maximum conductivity at least 30 orders in magnitude higher than its minimum conductivity.

Referring now to FIG. 7, an electrographic image may be developed by blowing a cloud of powder 5 against the photoconductive layer 24 simultaneously to the exposure of this layer to a light image and to the application of an alternating or an alternatively modulated electric voltage to electrodes 6 and 7. A cloud generator 35 is used to blow the powder; alternatively, rotating brushes or a spraying device may be used as well as any other means for gently blowing a cloud of powder against the pattern 2, 3 of original I. The amplitude of the modulated voltage is adjusted to electrically attract away the powder 12 which comes in contact with the conductive parts 2 of layer 24. while the powder 13 adheres to the least conductive parts of this layer. The layer 24 may be previously coated with a slight adhesive material to insure the adherence of the powder image 13. Moreover, a slight adhesive powder 5 may be used. The simultaneous application of the powder and of the electric voltage are prosecuted to obtain a uniform coat of powder 13 thus forming an electrographic image of high density on the least con ductive parts of the photoconductive layer 24. The duration of the development depends on the density of the powder cloud, although a stable image of good quality is generally obtained by applying from I to 5 complete periods of the modulated field. An excess of development will not change the obtained image, if a non-insulating powder 5 is used which has an electric conductivity superior to that of the least conductive parts of the pattern 2, 3. The other features of this method are substantially the same of those of the above described embodiments of the invention.

Referring now to FIG. 9, a sheet of copy material 8 is placed against the powder 13 of an electrographic image carried by the photoconductive layer 24 affixed to a transparent backing material 44. The sheet 8 and the layer 24 are interposed between a first electrode 6 and a transparent second electrode 7. The light of the sources 54 uniformly illuminate the photoconductive layer 24 to induce a uniform electric conductivity therein. An insulating layer 18 may be interposed between the sheet 8 and electrode 6 as well as a transparent second insulating layer (not shown) may be disposed between the backing material 44 and electrode 7, the powder 13 is charged from the uniformly illuminated layer 24 and electrically transferred on to the sheet 8. For example, an electric field may be generated which has an intensity from 3 to 30 v/micron in the gap 15 between the original 1 and the sheet '8. The satisfactory transfer of the powder image 13 is obtained by using a layer 24 uniformly excited to be at least 50 orders in magnitude more conductive than the material of the sheet 8. Thus for example, by using a layer 24 of amorphous selenium, a sheet 8 having an electric conductivity lower than 10" mho/cm will be used, such as a sheet of paper coated with polyvinyl chloride, for example. On the other hand, in accordance with the invention, an electrographic image is developed on a photoconductive non-insulating layer 24 (FIG. 6) in order to obtain, in the device of FIG. 9, the satisfactory transfer of the powder image from the non-insulating layer 24 on to a sheet of ordinary paper of copy; this type of paper is often constituted by a low insulating material having a conductivity from l0" to 10"" mho/cm. One of the above mentioned photoconductive non-insulating layers may be used; in order to obtain the satisfactory transfer, this type of layers may be excited to a conductivity of at least l0 mho/cm by an illumination of 10 lux, for example.

For carrying out the invention as described above, an apparatus of the type illustrated in FIG. 10 may be 10 used. This apparatus comprises a development station to form electrographic images from an original 1 provided with a conductivity pattern 2, 3 and a station 200 to transfer the electrographic images on to a web of copy material 8. In the example of FIG. 10, the original l is constituted by an endless belt 24, 44 formed by a transparent and flexible backing 44 on to which a photoconductive layer 24 is affixed. The apparatus comprises four rollers 10 over which the endless belt 24, 44 travels in the direction of arrow 110. A transparent insulating plate 47 is made of glass, for example, and it serves to guide the belt 24, 44. The transparent electrode 7 and the grid-electrode 6 are connected to the terminals of a voltage generator. A microfilm projector comprises a light source 41, an objective 3] and a film unroller 51 of which the unrolling direction is reversed that the endless belt 24, 44, as indicated by the arrow 210 and 110, respectively. In operation, the photoconductive layer 24 affixed to its flexible transparent support 44 is driven by rollers 10. The film 21 moves in the direction indicated by the arrow 210 whereas the photoconductive layer 24 and its support 44 moves in opposite direction with a synchroneous movement capable of immobilizing, in relation to the photoconductive layer 24, the optic image 2, 3 formed on the latter. The belt 24, 44 moving in the direction of arrow 110, the developer powder 5 of the container 25 uniformly coats the photoconductive layer 24 and a layer of powder 5 is driven by the upward movement of the latter in the electric field generated between electrodes 6 and 7. In order to insure the adherence of powder 6 to the layer 24, a slight adhesive powder 5 may be used, such as, for example, a powder 5 the grains of which are coated with zinc or aluminium stearate. Moreover, any other means having similar slight adherent qualities of holding the uniform layer of powder 5 may be used. Under the action of the electric field, the powder 12 coating the illuminated parts 2 of layer 24 is electrically attracted through the grid-electrode 6 and falls again in the container 25, while the powder 13 coating the low illuminated parts 3 forms a stable electrographic image thereon. If an excited layer 24 is used which is provided with a pattern 2, 3 having low differences in conductivity, an alternatively modulated voltage will be applied to electrodes 6 and 7. In this case, the time of passage of layer 24 under the grid-electrode 6 is two or three complete periods of the alternative modulation of the electric field. On the other hand, if the pattern 2, 3 has high differences in conductivity such as, for example, the above mentioned CDSEX7 layer excited by a light image from 2.5 to 20 lux, a direct electric voltage may be applied to electrodes 6 and 7; in this case the development of the stable electrographic image occurs in about 5 milliseconds, this lack of time including the response of layer 24 to the light (20 lux). By using a CDSEX7 layer, satisfactory electrographic images will be obtained at the maximum speed of 20m/sec if the optical image on layer 24 has a lenght of about 0.1 m in the direction of the movement of the belt 24,44. At the transfer station 200, the electrographic image 13 is transferred on to the web of copy 8. For example, the web 8 may be a web of copy paper driven against the layer 24 by the two rollers 20. An electric field is generated between the electrodes 26 and a second transparent electrode 27; the light source 54 uniformly illuminates the layer 24 across the electrode 27 and the backing 44. Under the combined action of the illumination of layer 24 and of the electric field generated between electrodes 26 and 27, the powder I3 is electrically charged from layer 24 and it is transferred on to the copy material 8.

According to another embodiment of the invention. an apparatus of the type illustrated in FIG. I] may be used to produce two copies from the same optical image forming a conductivity pattern 2, 3 in the photoconductive layer 24. The layer 24 is affixed to a flexible transparent support 44 and it is driven by rollers ID in the direction indicated by the arrow Ill). The apparatus of FIG. 1] comprises a powderer 400 to coat the layer 24 with a thin uniform layer of powder 5, a first development and transfer station 300 to develop a first stable electrographic image on a first material of copy 28 and a second stable electrographic image 13 on the least conductive parts of layer 24, and a second transfer station 200 to transfer said second image of powder 13 on to a second material of copy 8. The endless belt 24,44 moving in the direction of arrow 110, the developer powder of powderer 25 coats the layer 24 and the powder is driven by the upward movement of the latter between a grid-electrode 36 and a second electrode 37. Under the action of an electric field generated between electrodes 36 and 37, the excess of powder Sis charged from the remaining part of the layer of powder and it is electrically attracted through the grid-electrode 36 to fall again in the container 25; a thin uniform layer of powder 5 is thus obtained on the layer 24, rather than a particular amount of grains. Proceeding from powderer 400 to the first development and transfer station, the thin uniform layer of powder 5 is sandwiched between the layer 24 and the first material of copy 28. This material 28 may consist, for example, in a web of ordinary paper. The web 28 is driven agains layer 24 by two rollers 30. Under the action of an electric field generated between the electrodes 6 and 7, the powder 12 coating illuminated parts 2 of layer 24 is electrically transferred on to the first web of copy 28 to form a first stable electrographic image thereon, while the powder 13 forms a second stable electrographic image on the least conductive parts of layer 24. This second electrographic image is then transferred on to the second web of copy 8 at the second transfer station 200. The other features of the apparatus of FIG. 11 are the same as those above described with reference to the apparatus of FIG. 10.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not intended to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claimsv What I claim is:

1. A device for producing electrographic images from a conductivity pattern formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, comprising an insulating backing member onto which said conductivity pattern is affixed, means for coating said conductivity pattern with a thin layer of developer particles capable of receiving electric charges, an insulating layer against said conductivity pattern so that said coated conductivity pattern is electrically insulated between said insulating backing member and said insulating layer, means for generating an alternatively modulated electric field of sufficient strength across said insulating backing member and said insulating layer to transfer alternating electric charges from said conductivity pattern to said particles layer and to electrically attract particles having successive opposite polarities away from said conductivity pattern whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern by proceeding in the application of said electric field, and the remaining part of said particles is insufficiently charged so that it continues to coat said conductivity pattern whereby producing a stable electrographic image.

2. A device for producing electrographic images comprising a conductivity pattern including at least an area formed from a non-insulating material so that said conductivity pattern is formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, an insulating backing member onto which said conductivity pattern is affixed, means for coating said conductivity pattern with a thin layer of developer particles capable of receiving electric charges, an insulating layer against said conductivity pattern so that said coated conductivity pattern is electrically insulated between said insulating backing member and said insulating layer, means for generating an electric field of sufficient strength across said insulating backing member and said insulating layer to charge the particles coating said area formed from said non-insulating material in said conductivity pattern whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern and the remaining part of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image pattern.

3. A device for producing electrographic images comprising a photoconductive non-insulating layer, an insulating backing member onto which said photoconductive non-insulating layer is affixed, means for coating said photoconductive non-insulating layer with a thin layer of developer particles capable of receiving electric charges, an insulating layer placed against said photoconductive non-insulating layer so that said coated photoconductive non-insulating layer is electrically insulated between said insulating backing member and said insulating layer, means for exposing said pho toconductive non-insulating layer to an electromagnetic radiation to form a conductivity pattern in said photoconductive non-insulating layer, said conductiv ity pattern being formed by areas having differing elec tric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, means for generating an electric field of sufficient strength across said insulating backing member and said insulating layer to charge said particles whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern and the remaining part of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image.

4. A device for producing electrographic images on members of copy material, comprising a photoconductive non-insulating layer, an insulating backing member onto which said photoconductive non-insulating layer is affixed, means for coating said photoconductive noninsulating layer with a thin layer of developer particles capable of receiving electric charges, an insulating layer placed against said photoconductive noninsulating layer so that said coated photoconductive non-insulating layer is electrically insulated between said insulating backing member and said insulating layer, means for exposing said photoconductive noninsulating layer to an electromagnetic radiation to form a conductivity pattern in said photoconductive noninsulating layer, said conductivity pattern being formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity. means for generating an electric field of sufficient strength across said insulating backing member and said insulating layer to charge said particles whereby a portion of said particles is charged and removed from said conductivity pattern and a stable electrographic image is formed on said photoconductive noninsulating layer by the remaining part of said particles, means for removing said electrographic image bearing photoconductive non-insulating layer from said electric field, means for placing a copy material against the particles of said electrographic image, means for uniformly exposing said photoconductive non-insulating layer to an electromagnetic radiation inducing a uniform high electric conductivity in this photoconductive noninsulating layer, means for generating an electric field across said copy material and said photoconductive non-insulating layer to charge said particles from said uniformly conductive photoconductive noninsulating layer whereby said electrographic image is electrically transferred onto said copy material.

5. A device defined in claim 2 wherein said generating means comprises means for changing the direc tion of said electric field.

6. A device defined in claim 3 wherein said generating means comprises means for changing the direction of said electric field.

7. An electrographic device comprising a conductivity pattern formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, an insulating backing member onto which said conductivity pattern is affixed, a fluid insulating layer in juxtaposition to said conductivity pattern so that said conductivity pattern is electrically insulated between said insulating backing member and said fluid insulating layer, first and second electrode means between which are disposed said insulating backing member and said fluid insulating layer, at least one of said electrode means being a grid electrode, said grid electrode being in spaced relationship with said conductivity pattern and being juxtaposed to said fluid insulating layer, means for blowing a cloud of electri cally chargeable particles onto said conductivity pattern thereby coating the same, means for generating between said electrodes and across said fluid insulating layer and said insulating backing member an electric field of sufficient strength to charge said electrically chargeable particles whereby a portion of said electrically chargeable particles is sufficiently charged and removed from said conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image on said conductivity pattern said portion of said particles removed from said conductivity pattern migrating through the openings in said grid electrode and being removed from said electric field.

8. A device as defined in claim 7 wherein said generating means comprises means for changing the direction of said electric field.

9. A device as defined in claim 7 further comprising a photoconductive non-insulating layer and means for exposing said photoconductive non-insulating layer to an electromagnetic radiation so that said conductivity pattern is formed in said photoconductive noninsulating layer.

10. An electrographic device comprising a thin photoconcluctive non-insulating layer, an insulating backing member onto which said photoconductive noninsulating layer is affixed, a fluid insulating layer in juxtaposition to said photoconductive non-insulating layer so that said photoconductive non-insulating layer is electrically insulated between said insulating backing member and said fluid insulating layer, first and second electrode means between which are disposed said insulating backing member and said fluid insulating layer, at least one of said electrode means being a grid electrode, said grid electrode being in spaced relationship with said photoconductive non-insulating layer and being juxtaposed to said fluid insulating layer, means for blowing a cloud of electrically chargeable particles onto said photoconductive non-insulating layer thereby coating the same, means for exposing said photoconductive non-insulating layer to a first pattern of electromagnetic radiation to form a first conductivity pattern in said photoconductive non-insulating layer, said first conductivity pattern comprising areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, means for generating between said electrodes and across said fluid insulating layer and said insulating backing member a first electric field of sufficient strength to charge said electrically chargeable particles whereby a portion of said electrically chargeable particles is sufficiently charged and removed from said first conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said first conductivity pattern thereby producing a first stable electrographic image on said photoconductive non-insulating layer said portion of said particles removed from said first conductivity pattern migrating through the openings in said grid electrode and being removed from said electric field, said device further comprising means for blowing a second cloud of electrically chargeable particles onto said photoconductive non-insulating layer thereby coating the same, means for exposing said photoconductive non-insulating layer to a second pattern of electromagnetic radiation to form a second conductivity pattern in said photoconductive non-insulating layer, said second conductivity pattern comprising areas having differing conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, means for generating between said electrodes and across said fluid insulating layer and said insulating backing member a second electric field of sufficient strength to charge said electrically chargeable particles whereby a portion of said electrically chargeable particles is sufficiently charged and removed from said second conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said second conductivity pattern thereby producing a second stable electrographic image on said photoconductive non-insulating layer said portion of said particles removed from said second conductivity pattern migrating through the openings in said grid electrode and being removed from said second electric field.

ll. A device as defined in claim 10 wherein at least one of said generating means comprises changing the direction of said electric field,

l2. An electrographic device comprising a conductivity pattern including at least an area formed from a non-insulating material so that said conductivity pat tern is formed by areas having differing electric conductivity characteristics ranging from an area exhibit ing maximum conductivity to an area exhibiting minimum conductivity. an insulating backing member onto which said conductivity pattern is affixed, means for coating said conductivity pattern with a thin layer of electrically chargeable particles, an insulating image carrier against said layer of electrically chargeable particles so that said coated conductivity pattern is electrically insulated between said insulating backing member and said insulating image carrier, means for generating an electric field of sufficient strength across said insulating backing member and said insulating image car rier to charge said electrically chargeable particles whereby a portion of said electrically chargeable particles is sufficiently charged and removed from said conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image on said insulating image carrier by said portion of said particles removed from said conductivity pattern.

13. A device as defined in claim 12 further comprising a photoconductive non-insulating layer and means for exposing said photoconductive non-insulating layer to an electromagnetic radiation so that said conductivity pattern is formed in said photoconductive noninsulating layer.

14. A device as defined in claim 12 wherein said generating means comprises means for alternatively modu lating said electric field 15. An electrographic device comprising a photoconductive non-insulating layer, an insulating backing member onto which said photoconductive noninsulating layer is affixed, an electrographic image of electrically chargeable particles being formed on said photoconductive non-insulating layer. an insulating image carrier against said electrically chargeable particles so that said photoconductive noninsulating layer is electrically insulated between said insulating backing member and said insulating image carrier, means for exposing said photoconductive non-insulating layer to an electromagnetic radiation inducing a uniform high electric conductivity in said photoconductive noninsulating layer, means for generating an electric field across said insulating image carrier and said insulating backing member to charge the electrically chargeable particles of said electrographic image from said uniformly conductive photoconductive non-insulating layer whereby said electrographic image is electrically transferred onto said insulating image carrier.

16. A device as defined in claim 15 wherein said generating means comprises means for alternatively modulating said electric field.

17. An electrographic device comprising a conductivity pattern including at least an area formed from a non-insulating material so that said conductivity pattern is formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, an insulating backing member onto which said conductivity pattern is affixed, means for coating said conductivity pattern with a thin layer of electrically chargeable particles, a fluid insulating layer in juxtaposition to said conductivity pattern so that said coated conductivity pattern is electrically insulated be' tween said insulating backing member and said fluid insulating layer, first and second electrode means between which are disposed said insulating backing member and said fluid insulating layer, at least one of said electrode means being a grid electrode, said grid electrode being in spaced relationship with said conductivity pattern and being juxtaposed to said fluid insulating layer, means for generating between said electrodes and across said fluid insulating layer and said insulating backing member an electric field of sufficient strength to charge said electrically chargeable particles whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image on said conductivity pattern said portion of said particles removed from said conductivity pattern migrating through the openings in said grid electrode and being removed from said electric field.

18. A device as defined in claim 17 wherein said gen erating means comprises means for alternatively modulating said electric field.

19. An electrographic device comprising a photoconductive noninsulating layer, an insulating backing member onto which said photoconductive noninsulating layer is affixed, means for coating said photoconductive non-insulating layer with a thin layer of electrically chargeable particles, a fluid insulating layer in juxtaposition to said photoconductive non-insulating layer so that said coated photoconductive noninsulating layer is electrically insulated between said insulating backing member and said fluid insulating layer, means for exposing said photoconductive noninsulating layer to a pattern of electromagnetic radiation to form a conductivity pattern in said photoconductive non-insulating layer, said conductivity pattern comprising areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, first and second electrode means between which are disposed said insulating backing member and said fluid insulating layer, at least one of said electrode means being a grid electrode, said grid electrode being in spaced relationship with said conductivity pattern formed in said photoconductive non-insulating layer and being juxtaposed to said fluid insulating layer, means for generating between said electrodes and across said fluid insulating layer and said insulating backing member a first electric field of sufficient strength to charge said electrically chargeable particles whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image on said conductivity pattern said portion of said particles removed from said conductivity pattern migrating through the openings in said grid electrode and being removed from said first electric field, said device further comprising means for placing a copy material against the particles of said electrographic image, means for uniformly exposing said photoconductive non-insulating layer to an electromagnetic radiation in ducing a uniform high electric conductivity in said photoconductive non-insulating layer, means for generating a second electric field across said copy material and said photoconductive non-insulating layer to charge said particles from said uniformly conductive photo conductive non-insulating layer whereby said electrographic image is electrically transferred onto said copy material.

20. A device as defined in claim 19 wherein at least one of said generating means comprises means for al ternatively modulating said electric field.

21. An electrographic device comprising a photoconductive non-insulating layer, an insulating backing member onto which said photoconductive noninsulating layer is affixed, a fluid insulating layer in juxtaposition to said photoconductive non-insulating layer so that said photoconductive non-insulating layer is electrically insulated between said insulating backing member and said fluid insulating layer, first and second electrode means between which are disposed said insulating backing member and said fluid insulating layer, at least one of said electrode means being a grid elec trode, said grid electrode being in spaced relationship with said photoconductive non-insulating layer and being juxtaposed to said fluid insulating layer, means for placing a mass of electrically chargeable particles in contact with said photoconductive non-insulating layer, means for maintaining said photoconductive non-insulating layer in the dark and simultaneously generating between said electrodes and across said fluid insulating layer and said insulating backing memher a first electric field of sufficient strength to charge said electrically chargeable particles thereby forming a thin uniform layer of coating particles on said photoconductive non-insulating layer, means for removing said coated photoconductive non-insulating layer from said first electric field, an insulating layer placed against said photoconductive non-insulating layer so that said coated photoconductive non-insulating layer is electrically insulated between said insulating backing member and said insulating layer. means for exposing said photoconductive non-insulating layer to an elec tromagnetic radiation to form a conductivity pattern in said photoconductive non-insulating layer, said conductivity pattern being formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, means for generating a second electric field of sufficient strength across said insulating backing member and said insulating layer to charge said particles whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image.

22. A device as defined in claim 21 further comprising means for blowing said electrically chargeable particles through said grid electrode simultaneously with the generation of said first electric field so that said electrically chargeable particles are placed in contact with said photoconductive non-insulating layer.

23. A device as defined in claim 21 wherein at least one of said generating means comprises means for alternatively modulating said electric field,

24. An electrographic device comprising a noninsulating photoconductive layer provided with an electrographic image developed on said non-insulating photoconductive layer. an insulating backing onto which said non-insulating photoconductive layer is affixed, means for placing a copy material against the particles of said electrographic image so that said particles image is interposed between said copy material and said non-insulating photoconductive layer, means for exposing said non-insulating photoconductive layer to radiation inducing a high uniform conductivity in said non-insulating photoconductive layer, and means for generating across said copy material and said noninsulating photoconductive layer an electric field of sufficient strength to attract the particles of said electrographic image from said uniformly conductive noninsulating photoconductive layer onto said copy material. 

1. A device for producing electrographic images from a conductivity pattern formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, comprising an insulating backing member onto which said conductivity pattern is affixed, means for coating said conductivity pattern with a thin layer of developer particles capable of receiving electric charges, an insulating layer against said conductivity pattern so that said coated conductivity pattern is electrically insulated between said insulating backing member and said insulating layer, means for generating an alternatively modulated electric field of sufficient strength across said insulating backing member and said insulating layer to transfer alternating electric charges from said conductivity pattern to said particles layer and to electrically attract particles having successive opposite polarities away from said conductivity pattern whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern by proceeding in the application of said electric field, and the remaining part of said particles is insufficiently charged so that it continues to coat said conductivity pattern whereby producing a stable electrographic image.
 2. A device for producing electrographic images comprising a conductivity pattern including at least an area formed from a non-insulating material so that said conductivity pattern is formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, an insulating backing member onto which said conductivity pattern is affixed, means for coating said conductivity pattern with a thin layer of developer particles capable of receiving electric charges, an insulating layer against said conductivity pattern so that said coated conductivity pattern is electrically insulated between said insulating backing member and said insulating layer, means for generating an electric field of sufficient strength across said insulating backing member and said insulating layer to charge the particles coating said area formed from said non-insulating material in said conductivity pattern whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern and the remaining part of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image pattern.
 3. A device for producing electrographic images comprising a photoconductive non-insulating layer, an insulating backing member onto which said photoconductive non-insulating layer is affixed, means for coating said photoconductive non-insulating layer with a thin layer of developer particles capable of receiving electric charges, an insulating layer placed against said photoconductive non-insulating layer so that said coated photoconductive non-insulating layer is electrically insulated between said insulating backing member and said insulating layer, means for exposing said photoconductive non-insulating layer to an electromagnetic radiation to form a conductivity pattern in said photoconductive non-insulating layer, said conductivity pattern being formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, means for generating an electric field of sufficient strength across said insulating backing member and said insulating layer to charge said particles whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern and the remaining part of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image.
 4. A device for producing electrographic images on members of copy material, comprising a photoconductive non-insulating layer, an insulating backing member onto which said photoconductive non-insulating layer is affixed, means for coating said photoconductive non-insulating layer with a thin layer of developer particles capable of receiving electric charges, an insulating layer placed against said photoconductive non-insulating layer so that said coated photoconductive non-insulating layer is electrically insulated between said insulating backing member and said insulating layer, means for exposing said photoconductive non-insulating layer to an electromagnetic radiation to form a conductivity pattern in said photoconductive non-insulating layer, said conductivity pattern being formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, means for generating an electric field of sufficient strength across said insulating backing member and said insulating layer to charge said particles whereby a portion of said particles is charged and removed from said conductivity pattern and a stable electrographic image is formed on said photoconductive non-insulating layer by the remaining part of said particles, means for removing said electrographic image bearing photoconductive non-insulating layer from said electric field, means for placing a copy material against the particles of said electrographic image, means for uniformly exposing said photoconductive non-insulating layer to an electromagnetic radiation inducing a uniform high electric conductivity in this photoconductive non-insulating layer, means for generating an electric field across said copy material and said photoconductive non-insulating layer to charge said particles from said uniformly conductive photoconductive non-insulating layer whereby said electrographic image is electrically transferred onto said copy material.
 5. A device as defined in claim 2 wherein said generating means comprises means for changing the direction of said electric field.
 6. A device as defined in claim 3 wherein said generating means comprises means for changing the direction of said electric field.
 7. An electrographic device comprising a conductivity pattern formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, an insulating backing member onto which said conductivity pattern is affixed, a fluid insulating layer in juxtaposition to said conductivity pattern so that said conductivity pattern is electrically insulated between said insulating backing member and said fluid insulating layer, first and second electrode means between which are disposed said insulating backing member and said fluid insulating layer, at least one of said electrode means being a grid electrode, said grid electrode being in spaced relationship with said conductivity pattern and being juxtaposed to said fluid insulating layer, means for blowing a cloud of electrically chargeable particles onto said conductivity pattern thereby coating the same, means for generating between said electrodes and across said fluid insulating layer and said insulating backing member an electric field of sufficient strength to charge said electrically chargeable particles whereby a portion of said electrically chargeable particles is sufficiently charged and removed from said conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image on said conductivity pattern said portion of said particles removed from said conductivity pattern migrating tHrough the openings in said grid electrode and being removed from said electric field.
 8. A device as defined in claim 7 wherein said generating means comprises means for changing the direction of said electric field.
 9. A device as defined in claim 7 further comprising a photoconductive non-insulating layer and means for exposing said photoconductive non-insulating layer to an electromagnetic radiation so that said conductivity pattern is formed in said photoconductive non-insulating layer.
 10. An electrographic device comprising a thin photoconductive non-insulating layer, an insulating backing member onto which said photoconductive non-insulating layer is affixed, a fluid insulating layer in juxtaposition to said photoconductive non-insulating layer so that said photoconductive non-insulating layer is electrically insulated between said insulating backing member and said fluid insulating layer, first and second electrode means between which are disposed said insulating backing member and said fluid insulating layer, at least one of said electrode means being a grid electrode, said grid electrode being in spaced relationship with said photoconductive non-insulating layer and being juxtaposed to said fluid insulating layer, means for blowing a cloud of electrically chargeable particles onto said photoconductive non-insulating layer thereby coating the same, means for exposing said photoconductive non-insulating layer to a first pattern of electromagnetic radiation to form a first conductivity pattern in said photoconductive non-insulating layer, said first conductivity pattern comprising areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, means for generating between said electrodes and across said fluid insulating layer and said insulating backing member a first electric field of sufficient strength to charge said electrically chargeable particles whereby a portion of said electrically chargeable particles is sufficiently charged and removed from said first conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said first conductivity pattern thereby producing a first stable electrographic image on said photoconductive non-insulating layer said portion of said particles removed from said first conductivity pattern migrating through the openings in said grid electrode and being removed from said electric field, said device further comprising means for blowing a second cloud of electrically chargeable particles onto said photoconductive non-insulating layer thereby coating the same, means for exposing said photoconductive non-insulating layer to a second pattern of electromagnetic radiation to form a second conductivity pattern in said photoconductive non-insulating layer, said second conductivity pattern comprising areas having differing conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, means for generating between said electrodes and across said fluid insulating layer and said insulating backing member a second electric field of sufficient strength to charge said electrically chargeable particles whereby a portion of said electrically chargeable particles is sufficiently charged and removed from said second conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said second conductivity pattern thereby producing a second stable electrographic image on said photoconductive non-insulating layer said portion of said particles removed from said second conductivity pattern migrating through the openings in said grid electrode and being removed from said second electric field.
 11. A device as defined in claim 10 wherein at least one of said generating means comprises changing the direction of said electric field.
 12. An electrographic device comprising a conductivity pattern includIng at least an area formed from a non-insulating material so that said conductivity pattern is formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, an insulating backing member onto which said conductivity pattern is affixed, means for coating said conductivity pattern with a thin layer of electrically chargeable particles, an insulating image carrier against said layer of electrically chargeable particles so that said coated conductivity pattern is electrically insulated between said insulating backing member and said insulating image carrier, means for generating an electric field of sufficient strength across said insulating backing member and said insulating image carrier to charge said electrically chargeable particles whereby a portion of said electrically chargeable particles is sufficiently charged and removed from said conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image on said insulating image carrier by said portion of said particles removed from said conductivity pattern.
 13. A device as defined in claim 12 further comprising a photoconductive non-insulating layer and means for exposing said photoconductive non-insulating layer to an electromagnetic radiation so that said conductivity pattern is formed in said photoconductive non-insulating layer.
 14. A device as defined in claim 12 wherein said generating means comprises means for alternatively modulating said electric field.
 15. An electrographic device comprising a photoconductive non-insulating layer, an insulating backing member onto which said photoconductive non-insulating layer is affixed, an electrographic image of electrically chargeable particles being formed on said photoconductive non-insulating layer, an insulating image carrier against said electrically chargeable particles so that said photoconductive non-insulating layer is electrically insulated between said insulating backing member and said insulating image carrier, means for exposing said photoconductive non-insulating layer to an electromagnetic radiation inducing a uniform high electric conductivity in said photoconductive non-insulating layer, means for generating an electric field across said insulating image carrier and said insulating backing member to charge the electrically chargeable particles of said electrographic image from said uniformly conductive photoconductive non-insulating layer whereby said electrographic image is electrically transferred onto said insulating image carrier.
 16. A device as defined in claim 15 wherein said generating means comprises means for alternatively modulating said electric field.
 17. An electrographic device comprising a conductivity pattern including at least an area formed from a non-insulating material so that said conductivity pattern is formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, an insulating backing member onto which said conductivity pattern is affixed, means for coating said conductivity pattern with a thin layer of electrically chargeable particles, a fluid insulating layer in juxtaposition to said conductivity pattern so that said coated conductivity pattern is electrically insulated between said insulating backing member and said fluid insulating layer, first and second electrode means between which are disposed said insulating backing member and said fluid insulating layer, at least one of said electrode means being a grid electrode, said grid electrode being in spaced relationship with said conductivity pattern and being juxtaposed to said fluid insulating layer, means for generating between said electrodes and across said fluid insulating layer and said insulating backing member an electric field of sufFicient strength to charge said electrically chargeable particles whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image on said conductivity pattern said portion of said particles removed from said conductivity pattern migrating through the openings in said grid electrode and being removed from said electric field.
 18. A device as defined in claim 17 wherein said generating means comprises means for alternatively modulating said electric field.
 19. An electrographic device comprising a photoconductive non-insulating layer, an insulating backing member onto which said photoconductive non-insulating layer is affixed, means for coating said photoconductive non-insulating layer with a thin layer of electrically chargeable particles, a fluid insulating layer in juxtaposition to said photoconductive non-insulating layer so that said coated photoconductive non-insulating layer is electrically insulated between said insulating backing member and said fluid insulating layer, means for exposing said photoconductive non-insulating layer to a pattern of electromagnetic radiation to form a conductivity pattern in said photoconductive non-insulating layer, said conductivity pattern comprising areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, first and second electrode means between which are disposed said insulating backing member and said fluid insulating layer, at least one of said electrode means being a grid electrode, said grid electrode being in spaced relationship with said conductivity pattern formed in said photoconductive non-insulating layer and being juxtaposed to said fluid insulating layer, means for generating between said electrodes and across said fluid insulating layer and said insulating backing member a first electric field of sufficient strength to charge said electrically chargeable particles whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image on said conductivity pattern said portion of said particles removed from said conductivity pattern migrating through the openings in said grid electrode and being removed from said first electric field, said device further comprising means for placing a copy material against the particles of said electrographic image, means for uniformly exposing said photoconductive non-insulating layer to an electromagnetic radiation inducing a uniform high electric conductivity in said photoconductive non-insulating layer, means for generating a second electric field across said copy material and said photoconductive non-insulating layer to charge said particles from said uniformly conductive photoconductive non-insulating layer whereby said electrographic image is electrically transferred onto said copy material.
 20. A device as defined in claim 19 wherein at least one of said generating means comprises means for alternatively modulating said electric field.
 21. An electrographic device comprising a photoconductive non-insulating layer, an insulating backing member onto which said photoconductive non-insulating layer is affixed, a fluid insulating layer in juxtaposition to said photoconductive non-insulating layer so that said photoconductive non-insulating layer is electrically insulated between said insulating backing member and said fluid insulating layer, first and second electrode means between which are disposed said insulating backing member and said fluid insulating layer, at least one of said electrode means being a grid electrode, said grid electrode being in spaced relationship with said photocondUctive non-insulating layer and being juxtaposed to said fluid insulating layer, means for placing a mass of electrically chargeable particles in contact with said photoconductive non-insulating layer, means for maintaining said photoconductive non-insulating layer in the dark and simultaneously generating between said electrodes and across said fluid insulating layer and said insulating backing member a first electric field of sufficient strength to charge said electrically chargeable particles thereby forming a thin uniform layer of coating particles on said photoconductive non-insulating layer, means for removing said coated photoconductive non-insulating layer from said first electric field, an insulating layer placed against said photoconductive non-insulating layer so that said coated photoconductive non-insulating layer is electrically insulated between said insulating backing member and said insulating layer, means for exposing said photoconductive non-insulating layer to an electromagnetic radiation to form a conductivity pattern in said photoconductive non-insulating layer, said conductivity pattern being formed by areas having differing electric conductivity characteristics ranging from an area exhibiting maximum conductivity to an area exhibiting minimum conductivity, means for generating a second electric field of sufficient strength across said insulating backing member and said insulating layer to charge said particles whereby a portion of said particles is sufficiently charged and removed from said conductivity pattern and the remainder of said particles is insufficiently charged so that it continues to coat said conductivity pattern thereby producing a stable electrographic image.
 22. A device as defined in claim 21 further comprising means for blowing said electrically chargeable particles through said grid electrode simultaneously with the generation of said first electric field so that said electrically chargeable particles are placed in contact with said photoconductive non-insulating layer.
 23. A device as defined in claim 21 wherein at least one of said generating means comprises means for alternatively modulating said electric field.
 24. An electrographic device comprising a non-insulating photoconductive layer provided with an electrographic image developed on said non-insulating photoconductive layer, an insulating backing onto which said non-insulating photoconductive layer is affixed, means for placing a copy material against the particles of said electrographic image so that said particles image is interposed between said copy material and said non-insulating photoconductive layer, means for exposing said non-insulating photoconductive layer to radiation inducing a high uniform conductivity in said non-insulating photoconductive layer, and means for generating across said copy material and said non-insulating photoconductive layer an electric field of sufficient strength to attract the particles of said electrographic image from said uniformly conductive non-insulating photoconductive layer onto said copy material. 